Water electrolysis system

ABSTRACT

There is provided a water electro system which permits easy recycling of recovered pure water. The water electrolysis system includes: an electrolyte membrane  11  sandwiched by catalyst layers  12  and  13 ; a water electrolysis means  1  that brings out hydrogen from one catalyst layer and brings out a gas/liquid mixture of oxygen and pure water from the other catalyst layer by electrolyzing pure water; a gas/liquid separating means  2  that separates pure water  7  from the gas/liquid mixture; and a backflow means  8  that makes the separated pure water  7  flow back to the water electrolysis means  1 . The gas/liquid separating means  2  is arranged to be directly connected to a discharge opening  3  through which the gas/liquid mixture is brought out from the water electrolysis means  1 , and the gas/liquid mixture flows back directly to the gas/liquid separating means  2  through the discharge opening  3 . The water electrolysis system includes a purifying means  9  for purifying with the aid of ion exchange resin the pure water made to flow back by means of the backflow means  8 , and makes the purified pure water flow back to the water electrolysis means  1 . The purifying means  9  is arranged adjacently to the water electrolysis means  1 . The gas/liquid separating means  2  comprises an intake opening  4  for mint pure water. The gas/liquid separating means  2  comprises a filter  5  for separating oxygen and pure water from each other.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a water electrolysis cell thatproduces hydrogen by electrolyzing water.

[0003] 2. Description of the Related Art

[0004] As a water electrolysis system for producing hydrogen byelectrolyzing water, a system has hitherto been known which comprises astack of a plurality of water electrolysis cells each of which has sucha configuration that a solid polyelectrolyte membrane is sandwiched by apair of catalyst layers and a porous power feeder is laminated on eachof the catalyst layers. In the above described water electrolysissystem, pure water heated to the order of 80° C. is supplied to theabove described catalyst layers and porous power feeders of each of thewater electrolysis cells, and a voltage is applied to each of the porouspower feeders. In this way, oxygen and hydrogen ions are generated inthe anode section of each of the water electrolysis cells whereelectrolysis of water as represented by the following formula (1) occursto donate electrons to the electrode. The above described hydrogen ionsmove to the cathode section while penetrating through the abovedescribed solid polyelectrolyte membrane, and are given electrons fromthe electrode in the cathode section; consequently, hydrogen isgenerated in the cathode section of each of the water electrolysis cellsas represented by the following formula (2).

2H₂O→O₂ ↑t+4H⁺+4e⁻  (1)

2H⁺+4e⁻→H₂↑  (2)

[0005] Thus, in the above described water electrolysis system, thehydrogen generated in the above described cathode section of each of thewater electrolysis cells is brought out and provided to certainprescribed applications. The above described hydrogen is utilized, forexample, as fuel for fuel cells.

[0006] On the other hand, in the above described water electrolysissystem, the oxygen generated in the anode section of each of the waterelectrolysis cells is brought out as a gas/liquid mixture of oxygen andpure water. In this context, the above described pure water is high inprice, which is separated from the oxygen by means of a gas/liquidseparating unit, and thus recovered and subjected to recycling (forexample, see Japanese Patent Laid-Open No. 8-260176). In the abovedescribed conventional water electrolysis system, the above describedgas/liquid separating unit is arranged in a manner independent of theabove described water electrolysis cell stack, and is connected to thewater electrolysis cell stack through piping.

[0007] In the above described conventional water electrolysis system,however, the recovered pure water cannot avoid degradation in purity aswater, and hence is accompanied by a problem that the recovered purewater can hardly be subjected to recycling as it is.

SUMMARY OF THE INVENTION

[0008] The present invention takes as its object the provision of awater electrolysis system in which such a problem as described above isovercome and the recovered pure water can be easily subjected torecycling.

[0009] For the purpose of achieving the above described object, thewater electrolysis system of the present invention comprises a waterelectrolysis system comprising a water electrolysis means that comprisesa pair of catalyst layers and an electrolyte membrane sandwiched by bothof the catalyst layers, electrolyzes pure water supplied to the catalystlayers, and brings out hydrogen from one catalyst layer and brings out agas/liquid mixture of oxygen and pure water from the other catalystlayer, a gas/liquid separating means for separating pure water from thegas/liquid mixture of oxygen and pure water both brought out from saidwater electrolysis means, and a backflow means for making the purewater, separated by said gas/liquid separating means, flow back to thewater electrolysis means, wherein the gas/liquid separating means isarranged to be directly connected to a discharge opening through whichthe gas/liquid mixture of oxygen and pure water is brought out from saidwater electrolysis means, and the gas/liquid mixture directly flows intothe gas/liquid separating means through the discharge opening.

[0010] In the water electrolysis system of the present invention, theabove described gas/liquid separating device is directly connected tothe discharge opening through which the gas/liquid mixture of oxygen andpure water is brought out from the above described water electrolysisdevice, and accordingly the above described gas/liquid mixture is madeto flow from the above described discharge opening directly into thegas/liquid separating device so that it is not necessary to connect thegas/liquid separating device to the water electrolysis device throughpiping. Consequently, the pure water supplied to the above describedwater electrolysis device is made to flow directly into the gas/liquidseparating device as a gas/liquid mixture of the pure water and theabove described oxygen after having been subjected to electrolysis sothat the temperature decrease and the purity degradation as water can besuppressed.

[0011] Thus, according to the water electrolysis system of the presentinvention, the recovered pure water can be easily subjected torecycling. Additionally, according to the water electrolysis system ofthe present invention, the temperature decrease of the recovered purewater is suppressed, and hence it is not necessary to use a heatingdevice such as a heater for heating the pure water so that the energyefficiency can be enhanced.

[0012] Additionally, it is preferable that the water electrolysis systemof the present invention comprises a purifying means for purifying withthe aid of ion exchange resin the pure water made to flow back by meansof the above described backflow means, and the pure water having beenpurified by the purifying means is made to flow back to the abovedescribed water electrolysis means. According to the water electrolysissystem of the present invention, the recovered pure water is suppressedas described above in degradation of the purity as water. Consequently,it suffices that the recovered pure water is purified by use of such asimple and easy to use means as above described ion exchange resin whenthe recovered pure water is made to flow back to the above describedwater electrolysis means by the above described backflow means, and thusthe recovered pure water can easily recover the purity required for theabove described electrolysis. Additionally, by adopting this way, theenergy which would be required for newly producing pure water can be cutdown. Making the above described purifying means be arranged adjacent tothe above described water electrolysis means permits cutting down thepiping, and accordingly permits suppressing the temperature decrease anddegradation of purity as water of the recovered pure water.

[0013] Additionally, it is preferable that in the water electrolysissystem of the present invention, the above described gas/liquidseparating means comprises an intake opening for mint pure water to besupplied to the above described water electrolysis means. By adoptingthis way, mint pure water is supplied to the above described gas/liquidseparating means from the above described intake opening, and made tomerge with the above described recovered pure water within thegas/liquid separating means to be supplied to the above described waterelectrolysis means. Accordingly, the backflow means for the abovedescribed recovered pure water and a supply means for supplying mintpure water to the above described water electrolysis means are made toshare the same means, and the system configuration can thereby besimplified.

[0014] Additionally, it is preferable that the above describedgas/liquid separating means comprises a filter for separating oxygen andpure water from each other. The above described gas/liquid separatingmeans can efficiently separate, using a small operation volume, oxygenand pure water from each other owing to provision of the above describedfilter. As the above described filter, for example, a stainless-steelmesh can be used.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is an illustrative sectional view of a water electrolysissystem of an embodiment of the present invention; and

[0016]FIG. 2 is an enlarged illustrative sectional view of the main partof the water electrolysis system shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] Further detailed description will be made below of an embodimentof the present invention with reference to the accompanying drawings.

[0018] The water electrolysis system of the present embodiment comprisesa water electrolysis cell stack 1 and a gas/liquid separating unit 2that is arranged in direct contact with one side face of the waterelectrolysis cell stack 1 without the intermediary of piping as shown inFIG. 1. The gas/liquid separating unit 2 is provided with a gas/liquiddischarge opening 3 between the water electrolysis cell stack 1 and theseparating unit 2 through which a gas/liquid mixture of oxygen and purewater is brought out from the water electrolysis cell stack 1.

[0019] Additionally, the gas/liquid separating unit 2 comprises a purewater intake opening 4 for bringing in mint pure water, a filter 5 forseparating the above described gas/liquid mixture into oxygen and purewater, and an oxygen discharge opening 6 for releasing the separatedoxygen into the atmosphere. Incidentally, the filter 5 is made ofstainless-steel mesh.

[0020] The water electrolysis system of the present embodiment furthercomprises a pump 8 beneath the gas/liquid separating unit 2. The pump 8makes the pure water 7 separated from the above described gas/liquidmixture flow back to the water electrolysis cell stack 1 through a duct8 a arranged along the bottoms of the water electrolysis cell stack 1and gas/liquid separating unit 2. Besides, a purifying unit 9 forpurifying the pure water, made to flow back by the pump 8, by means ofion exchange resin is arranged adjacent to the water electrolysis cellstack 1, in a manner interposed in a midway portion of the duct 8 a.

[0021] The water electrolysis cell stack 1 is provided with, on onehand, the oxygen discharge opening 3 and, on the other hand, a hydrogendischarge opening 10 for bringing out the hydrogen generated byelectrolysis. Additionally, as FIG. 2 shows, the water electrolysis cellstack 1 has such a configuration that a solid polyelectrolyte membrane11 is sandwiched by a pair of catalyst layers 12 and 13, porous powerfeeders 14 and 15 are provided respectively over the catalyst layers 12and 13, and a plurality of water electrolysis cells 16 are laminatedthrough separators 17 which serves as a gas/liquid passage.

[0022] In the above described water electrolysis cell 16, the catalystlayers 12 and 13 are formed, for example, by screen printing apaste-like substance, obtained by dispersing a prescribed amount of acatalyst powder in an electrolyte solution that dissolves an electrolytehaving the same component as the solid polyelectrolyte membrane 11, ontoa sheet made of polytetrafluoroethylene. Additionally, by hot pressingunder the condition that the solid polyelectrolyte membrane 11 issandwiched with the surfaces of the above described sheet on which thecatalyst layers 12 and 13 are formed, the catalyst layers 12 and 13 aretranscribed respectively onto the surfaces of the solid polyelectrolytemembrane 11 and thereby bonded to the solid polyelectrolyte membrane 11.

[0023] In the next place, description will be made of the operation ofthe water electrolysis system of the present embodiment.

[0024] In the water electrolysis system of the present embodiment, atthe beginning, mint pure water heated to the order of 80° C. is suppliedfrom the pure water intake opening 4 in the gas/liquid separating unit2, and supplied with the aid of the pump 8 to the water electrolysiscell stack 1 through the intermediary of the purifying unit 9, andsubjected to electrolysis. Consequently, hydrogen is generated from thecathode section of each of the water electrolysis cells 16 constitutingthe water electrolysis cell stack 1, and brought out to the outside fromthe hydrogen discharge opening 10 of the water electrolysis cell stack1. On the other hand, oxygen is generated from the anode section of eachof the water electrolysis cells 16, and the oxygen forms with pure watera gas/liquid mixture, which flows from the gas/liquid discharge opening3 directly into the gas/liquid separating unit 2.

[0025] In this context, the pure water contained in the above describedgas/liquid mixture directly flows into gas/liquid separating unit 2 fromthe water electrolysis cell stack 1 through the gas/liquid dischargeopening 3, and hence the temperature decrease scarcely occurs and thepurity as water is hardly degraded.

[0026] In the next place, the above described gas/liquid mixture isseparated into oxygen and pure water, by means of the filter 5 made ofstainless-steel mesh in the gas/liquid separating unit 2. Then, theabove described oxygen is released into the atmosphere from the oxygendischarge opening 6, while the above described pure water is stored inthe gas/liquid separating unit 2 below the filter 5. Incidentally, thepure water 7 stored in the gas/liquid separating unit 2 is made to mergewith mint pure water supplied from the pure water intake opening 4.

[0027] In the next place, the pure water 7 stored in the gas/liquidseparating unit 2 is brought out with the aid of the pump 8 from thegas/liquid separating unit 2, transferred to the purifying unit 9,purified with the aid of ion exchange resin and thereby recovers thepurity as high as that of the mint pure water. The pure water thuspurified is supplied from the purifying unit 9 to the water electrolysiscell stack 1 to be again subjected to electrolysis.

[0028] Consequently, according to the water electrolysis system of thepresent embodiment, the pure water recovered from the gas/liquid mixturegenerated in the water electrolysis cell stack 1 can be easily andeffectively subjected to recycling.

What is claimed is:
 1. A water electrolysis system comprising: a waterelectrolysis means that comprises a pair of catalyst layers and anelectrolyte membrane sandwiched by both of the catalyst layers,electrolyzes pure water supplied to said catalyst layers, and brings outhydrogen from one catalyst layer and brings out a gas/liquid mixture ofoxygen and pure water from the other catalyst layer; a gas/liquidseparating means for separating pure water from the gas/liquid mixtureof oxygen and pure water both brought out from said water electrolysismeans; and a backflow means for making the pure water, separated by saidgas/liquid separating means, flow back to said water electrolysis means;wherein: said gas/liquid separating means is arranged to be directlyconnected to a discharge opening through which the gas/liquid mixture ofoxygen and pure water is brought out from said water electrolysis means;and said gas/liquid mixture directly flows into said gas/liquidseparating means through said discharge opening.
 2. The waterelectrolysis system according to claim 1, comprising a purifying meansfor purifying with the aid of ion exchange resin the pure water made toflow back by said backflow means, wherein pure water having beenpurified by said purifying means is made to flow back to said waterelectrolysis means.
 3. The water electrolysis system according to claim2, wherein said purifying means is arranged adjacent to said waterelectrolysis means.
 4. The water electrolysis system according to claim1, wherein said gas/liquid separating means comprises an intake openingfor mint pure water to be supplied to said water electrolysis means. 5.The water electrolysis system according to claim 1, wherein saidgas/liquid separating means comprises a filter for separating oxygen andpure water from each other.